<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        input {
            color: #999;
        }
    </style>
</head>

<body>
    <input type="text" value="手机">

    <script>
        //1.获取元素
        var text = document.querySelector('input');
        //2.注册事件，获得焦点事件 onfocus
        text.onfocus = function () {
            // console.log('得到了焦点');
            if (this.value === '手机') {
                this.value = '';   //把value值清空即可
            }
            //获得焦点后需要把文本框里面的文字颜色变黑
            this.style.color = '#333';

        }


        //3.注册事件，失去焦点onblur
        text.onblur = function () {
            // console.log('失去焦点');
            if (this.value === '') {
                this.value = '手机';
            }
            this.style.color = '#999';  //失去焦点：需要把文本框里面的文字颜色变浅色
        }

    </script>
</body>

</html>